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Semester 2 Year 1 > Excitation Contraction Coupling > Flashcards

Excitation Contraction Coupling Flashcards

1
Q

What is excitation contraction coupling?

A

Linkage between excitation of muscle fibre membrane and onset of contraction

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2
Q

What is action potential like in skeletal muscle?

A

Very fast - 10msec

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3
Q

Tension response vs Action potential in skeletal muscle:

A

Latent period between both

Contraction of muscle doesn’t overlap with AP

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4
Q

Where does latent period take place in skeletal muscle?

A

At peak of AP and start of contraction

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5
Q

What happens during latent period?

A

Effect of changed membrane potential

Diffusion of signalling substance from extracellular space

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6
Q

What effect does change in membrane potential do in latent period of skeletal muscle?

A

Electrical field change is limited to immediate vicinity (surrounding) of plasma membrane

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7
Q

Why is the diffusion of signalling substance from extracellular space highly unlikely to cause latent period in skeletal muscle?

A

Time for diffusion much longer than latent period

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8
Q

What does T-system enable?

A

Delivery of action potential deep into muscle fibre

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9
Q

Where is calcium stored?

A

Sarcoplasmic reticulum

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10
Q

What happens when action potential arrives at axon terminal in neuromuscular junction?

A

Acetylcholine diffuses across synaptic cleft and binds to nicotinic receptors

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11
Q

What are nicotinic receptors like?

A

Ligand-gated channels

2 molecules of ACh bind to each receptor

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12
Q

What happens when acetylcholine binds to nicotinic receptors?

A

They open and Na+ floods in (outweighs K+ moving out)

Cell depolarises

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13
Q

What happens after depolarisation of motor end plate?

A

AP propagates along surface of muscle fibre - sarcolemma

AP propagates down T-tubule membrane

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14
Q

What happens after action potential propagates down T-tubule?

A

Conformational change of DHP receptor

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15
Q

What happens when DHP receptor changes shape?

A

Foot processes pull open RYR receptor (calcium release channel)

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16
Q

What happens after RYR channel opens?

A

Calcium ions diffuse out of sarcoplasmic reticulum and flood into cytosol (down conc. gradient)

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17
Q

What helps calcium release from sarcoplasmic reticulum?

A

Calcium-binding protein called calsequestrin

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18
Q

What happens in latent period in skeletal muscle in regards to calcium?

A

There is an increase in intracellular calcium concentration

This causes muscle contraction

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19
Q

How is calcium recycled in skeletal muscle?

A

Sarcoplasmic reticulum / terminal cisternae

Cytoplasm

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20
Q

What are the two junctional foot proteins?

A

DHPR

RYR

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21
Q

What does DHPR stand for?

A

Dihydropyridine receptor protein

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22
Q

What type of receptor is DHPR?

A

L-type voltage-gated calcium channel

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23
Q

Where is DHPR receptor found?

A

T-tubule membrane

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24
Q

What does RYR stand for?

A

Ryanodine receptor protein

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25
Q

What type of receptor is RYR?

A

Calcium release channel into sarcoplasmic reticulum

26
Q

What happens after calcium enters cytoplasm?

A

Binds to troponin C

Allows strong actin-myosin binding

27
Q

What concentration does cytoplasmic calcium increase to?

A

10-7 M to 10-5 M

28
Q

What’s the key event resulting in interaction of actin and myosin filaments?

A

The increase in intracellular calcium concentration

29
Q

Example of dihydropyridine:

A

Nifedipine

30
Q

What muscle does Nifedipine address?

A

Smooth muscle

31
Q

What is nifedipine used to treat in smooth muscle?

A

Hypertension

Migraine

Atherosclerosis

32
Q

What is What is Nifedipine?

A

Voltage-gated calcium channel blocking drug

33
Q

Example of ryanodine:

A

Dantrolene

34
Q

What does Dantrolene do?

A

Spasmolytic drug acting as skeletal muscle relaxant

Acts of ryanodine receptor

35
Q

What area in muscle does dantrolene address?

A

Sarcoplasmic reticulum

36
Q

What is dantrolene used to treat?

A

Muscle spasm

Malignant hyperthermia

37
Q

What’s needed in order for relaxation of skeletal muscle?

A

Repolarisation

Removal of calcium bac to resting levels

38
Q

What helps to return calcium back to resting levels?

A

Calcium ATPase (SERCA)

39
Q

What does SERCA stand for?

A

Sarcoplasmic endo plastic reticulum calcium ATPase

40
Q

What does SERCA do?

A

Forces calcium against concentration gradient

41
Q

What type of process is SERCA uptake?

A

Active process - need energy from hydrolysis of ATP

42
Q

What activates the SERCA pump in sarcoplasmic reticulum membrane?

A

Increase in intracellular calcium concentration

43
Q

How much calcium does SERCA actively transport?

A

2 calcium ions per molecule of ATP hydrolysed

44
Q

What does calcium concentration in cytoplasm decrease to after removed via SERCA?

A

Back to 10-7 M (resting levels)

45
Q

What is the role of calsequestrin?

A

Stores calcium at high concentrations in terminal cisternae

46
Q

What does the storing of calcium in calsequestrin result in?

A

Concentration gradient from sarcoplasmic reticulum to cytoplasm

47
Q

How many calcium ions bind to calsequestrin?

A

23 calcium ions per molecule

48
Q

Why don’t muscle cells in heart need an action potential to drive contraction?

A

Pacemaker cells - set electrical rhythm

49
Q

WHat are pacemaker cells?

A

Specialised muscle cells

50
Q

What is the resting potential like in pacemaker cells?

A

Unstable

51
Q

WHat do pacemaker cells undergo?

A

Automatic rhythmical depolarisation

52
Q

What is depolarisation of pacemaker potentials like?

A

They always depolarise to threshold

Fast

53
Q

Graph of action potential in cardiac muscle:

A

Fast initial depolarisation

Partial repolarisation and then plateau due to influx of calcium

54
Q

Duration of AP in cardiac muscle compared to in skeletal muscle:

A

Much longer - 350 ms

55
Q

How is change in tension different in cardiac muscle to skeletal muscle?

A

There is a change in tension during action potential - an overlap

56
Q

Where does 25% of required calcium for contraction go?

A

Enters through L-type calcium channels (DHPR) in T-tubule membrane

57
Q

What happens when 25% of calcium enters DHPR receptors in cardiac muscle?

A

Binds to RYR receptors + trigger calcium from stores

Calcium released via RYR channels in sarcoplasmic reticulum

58
Q

How is relationship between DHR and RYR different in cardiac muscle to skeletal muscle?

A

No mechanical coupling

It’s called calcium-induced calcium release

59
Q

Describe Calcium-indicted Calcium release:

A

25% Calcium enters DHPR channel

Calcium binds to RYR receptor

RYR receptor opens and 75% calcium released from sarcoplasmic reticulum

60
Q

What does relaxation of cardiac muscle require?

A

Decrease in cytoplasmic calcium concentration to 10-7 M

61
Q

What happens when cytoplasmic calcium concentration decreases?

A

Calcium ATPase in sarcoplasmic reticulum is activated

62
Q

What also helps remove calcium from cytoplasm?

A

Sodium:Calcium exchange in sarcolemma membrane

Requires sodium ATPase

Semester 2 Year 1 (12 decks)

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